Display screen or portion thereof with a graphical user interface



The FIGURE is a front view of a display screen or portion thereof with agraphical user interface in accordance with my design.

The broken lines shown in the drawing illustrate a mobile device andportions of the display screen or portion thereof with a graphical userinterface that forms no part of the claimed design.

CLAIM The ornamental design for a display screen or portion thereof witha graphical user interface, as shown and described.